It is known that in modern fluid jet looms (air and water looms) it has become of common use to employ measuring weft feeders equipped with their own electric motor and with a system to control and stop the amount of weft yarn supplied to the loom at each weft picking.
Such measuring weft feeders usually comprise: an electric motor allowing, by means of a rotary member (winding reel), to draw the weft yarn from the spool and wind the same into turns, evenly arranged on the outer surface of a winding unit; means (sensors) to control the amount of weft yarn present on the winding unit, and means (photoelectric cells) to control the weft yarn turns being unwound; and one or more devices, usually of the electromagnetic type, to stop the weft yarn being unwound so as to block the same after weft picking.
Two different systems are adopted, at present, to feed the loom with the right length of weft yarn required for the weaving being performed, said length mainly depending on the width of the fabric being woven, but also on the type of fabric and on the type of yarns used for weaving the same. In fact, the measuring weft feeders can be of two types: the type which comprises a unit for winding up a fixed length of weft yarn reserve turns, namely a cylinder of fixed diameter commonly called a drum, and which uses a plurality of devices to stop the yarn, positioned evenly spaced over a ring around the drum; and the type which uses instead a single device to stop the weft yarn, but wherein use has to be made of a winding unit with variable turn length, this latter being adjustable each time according to the weft yarn length having to be inserted into the loom shed.
In the first type of measuring weft feeder, the adjustment of the weft yarn length L to be picked is performed by counting the number of whole turns contained in L and selecting, for each weft picking, the electomagnetic stopping device having to be operated, so that its angular position may correspond to the turn fraction closest to the value required to complete the length L: in this way it is possible to perform a stepwise adjustment of the length L, essentially by electronic means.
In the second type of measuring weft feeder, the adjustment of the length L of weft yarn to be picked is instead performed by varying the length of the turns on the winding unit through shifting of a discrete number of movable rods which form, in combination with a fixed cylinder, the aforespecified unit or drum; on said drum, the weft yarn is generally wound along a polygonal path, the length of which is equal to the length of a whole turn of wound yarn.
The present invention relates to improvements in this second type of measuring weft feeder and it concerns, in particular, the adjustment of the turn length on its winding unit or drum (namely, the adjustment of the diameter of this latter).
Up to the present, in the measuring weft feeders of the type being considered, the adjustment of the turn length on the winding unit has generally been performed by manually changing the radial position of the single rods (or--in the event of these being assembled so as to form a plurality of sectors--the position of the single sectors), so as to suitably draw the movable rods either toward or away from the fixed cylinder.
It is evident that the manual adjustment of the position of the single rods (or of sectors or groups thereof) involves a certain effort on the operator's part, in that it requires separately adjusting the position of the single elements, thereby guaranteeing, as well as the right turn length, also the regularity of the polygonal path being followed by the reserve turn when it winds around said rods. Said regularity is a very important condition for the proper working of the measuring weft feeder, since the closer the polygonal path approaches a circular shape, the easier it is for the weft yarn to be unwound at high speed, preventing tears and tension changes which may be determined by sudden variations in the curvature radius of the outer surface of the winding unit.
In conclusion, whenever having to vary the turn length on the winding unit or drum of known measuring weft feeders, the operator is forced to perform an exacting work with a considerable waste of time, and the adjustment obtained is often not as efficient as it should be, which can cause great inconveniences especially as to loom productivity and quality of the fabric.